The crankset is one of the main components of the bicycle drive chain and it’s used to transfer motion of the rider’s legs into a rotational motion. The motion used to drive the chain then turns the rear wheel. In the centre of the crankset is a set of bearings that will ensure the crank arms run in a smooth rotation when the bike is being pedalled.
Over time the bearings will wear out as they grind against each other, making it harder for the crank to turn. Before the crank bearings are changed, it’s important that you understand the types of bottom brackets available and how to remove and replace the crank bearings.
THE DIFFERENT TYPES OF BOTTOM BRACKETS
The crank bearings are part of the bottom bracket assembly that slots into the round bottom bracket shell on the bicycle frame. This part will contain the spindle that is the axle of the crankset; this part allows the bearings to move smoothly. The crank bearings are connected via spindles with one being attached on the surface and one onto the frame.
There are a number of different bottom bracket configurations. Older bicycles tend to have something known as a cup and cone bracket. Whereas many new bicycles, use cartridge bottom brackets.
Types of Bottom Brackets
- Loose Bearings – Three piece assembly with separate spindle and cranks
- Cartridge – Sealed units holding the bearings and the spindle
- One Piece – Spindle and crank arms are a single piece with bearings pressed into the bottom bracket shell
- Pressed Bearings – Bottom bracket with bearings pressed directly into the bicycle frame
REMOVING THE CRANK BEARINGS
Changing bicycle crank bearings is quite a simple process and it involves removing the old unit and inserting a new one. Removing crank bearing assemblies will require special tools such as bottom bracket tools or crank pullers. Cup and cone assemblies will usually require a long ring spanner and pin spanner.
Replacing the cartridge crank bearing will begin by removing the crank arms. Next use the bottom bracket tools to unscrew the old unit. Modern bicycle bearing uses a reverse thread on the bottom bracket and will involve unscrewing it in a clockwise direction.
Cup and Cone Removal
When removing a cup and cone assembly you will need to begin by removing the lock ring with a specialist spanner; this will free the cup for removal. Then you should use the pin spanner or a chisel and mallet to unscrew the cup. Once the cup is removed, you can take out the bearings.
At this stage, it’s important to take note of the way the bearings retainer comes out. The new bearings should be put in the same way. The cup on the right side of the bracket should be left on the bottom bracket; leaving this part will eliminate any accidental damage being caused.
Preparing The Bottom Bracket
Before installing a new crank bike bearing and reassembling the bike, the bottom bracket should be thoroughly cleaned. Use a specialist solvent degreaser to degrease the congealed grease and remove any grit. When doing this make sure the threads are in good condition.
REPLACING THE CRANK BEARINGS
When it comes to replacing cartridge bottom brackets, simple grease the threads of the bottom bracket shell and screw the assembly back into the frame. The ball bearings retainer should be thoroughly cleaned and the re-greased. When bearings are inserted into the retainer, the bottom bracket should also be re-greased.
The ball bearings should be placed into the right side bearings into the bottom bracket. The spindle should be cleaned and then reinserted into the bottom bracket, ensuring that the orientation is asymmetrical. The left side bearings can then be greased and the cup reattached. Using the tools to ensure the parts are secure.
Frequently Asked Questions About Changing Crank Bearings
How to Change the Crank on a Bike?
After making sure your chain is hooked back onto the chainring, you can now slide your new cranks into place. Start with the right crank and then the left, making sure they’re in the ‘12 and 6’ position. The next step is to then replace the bolt and re-tighten them with your torque wrench until you hear a click. Remember to check that the newton metre matches the recommendation in your bike owner’s manual beforehand.
The last step is to re-attach the bike pedals, be sure to coat the threads with grease as this will keep them turning and make it easier to take them off the next time. Finally, tighten them back up with your pedal spanner.
How to Remove Bottom Bracket Bearings?
Inspect the threaded cups for tool fittings. There are many different designs and tool options. When you have the correct tool which is needed, insert the tool fully and remove the non-drive (left-side) cup by turning counterclockwise, holding the tool firmly to the cup. Removing an internal sleeve, it’s important to take note of any spacers under the cup for reassembly. For more information on bike maintenance, check out our articles.
How to Remove Bike Crank?
To remove your bike cranks you will need an Allen bolt, this will need to match the bolt that connects your bike cranks to the bottom bracket. You can usually find the correct size for this in your bike’s user manual or you can try out the bolt for size if you’ve got an Allen bolt set. Simply loosen the bolt and take it off.
The next step is to take your crank extractor. It is important to add plenty of greases to lubricate your crank extractor before inserting and tighten it with your spanner to prevent any damage to the threads. Once your crank extractor is nice and tight, give it a turn until it comes off the bike.
Repeat this on the other side.